Hood lift mechanisms utilizing active materials and methods of use

ABSTRACT

A cam lift and reset assembly includes a cam mounted on a rotatable shaft having a cam profile effective to provide a lifting force to a contacted part thereon upon rotation of the shaft and movement of the cam profile of the cam relative to the contacted part from a rest position to a lift position. The assembly also includes an active material in operative communication with the shaft, the active material being operative to change at least one property of the active material in response to an activation signal so as to effect rotation of the shaft. The assembly further includes a reset device in operative communication with the shaft to provide a reset force to the contacted part and counter-rotation of the shaft and movement of the cam profile of the cam relative to the contacted part from the lift position to the rest position.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part application of U.S. patentapplication Ser. No. 11/533,422 filed Sep. 20, 2006, which is acontinuation-in part of Ser. No. 11/430,794 filed on May 9, 2006, andU.S. patent application Ser. No. 10/864,724 filed on Jun. 4, 2004, whichare hereby incorporated herein by reference in their entireties.

BACKGROUND

The present disclosure generally relates to a hood lift mechanism foruse in an automotive vehicle, wherein the hood lift mechanism includesthe use of active materials. Also disclosed is control logic forreversibly and selectively activating the active material based hoodlift mechanism.

Numerous motor vehicles employ a hingeable hood disposed in a regionbetween the passenger compartment and the forward bumper of the motorvehicle, or between the passenger compartment and the rearward bumper ofthe motor vehicle. The hingeable hood provides a mechanism for accessingthe underlying engine or storage compartment. The hingeable hood istypically formed of a relatively thin sheet of metal or plastic that ismolded to the appropriate contour corresponding to the overall vehiclebody design. Owing to the relatively thin nature of the material formingthe hingeable hood, a support structure such as a contoured plate withstamped rib supports typically extends across the underside of the hoodportion so as to provide a degree of dimensional stability to thestructure.

Aerodynamics, styling, and packaging considerations, among others, haveall contributed to the design of the front ends and hood regions ofcurrent vehicles. Aerodynamic drag (and fuel economy considerations) inparticular has contributed to the hood being in close proximity to theengine or storage compartment. Accordingly, hood deformation such asthat which may occur upon impact of an object onto the hood, and thusthe ability of the hood to absorb energy at appropriate force levelsbefore bottoming out against hard objects beneath it, is somewhatlimited by the contents of the compartment.

In response, automobile manufacturers have proposed a number ofmechanisms that change the orientation and/or position with respect tothe vehicle of the hood before a deformation event such as the impactevent previously described. For example, hood lifters may be activatedby impact sensors to increase the space between the hood and theunderlying compartment. The hood lifters change the orientation of thehood by raising it (in most mechanisms by raising it at a rear edgewhile maintaining attachment of a front edge to the vehicle structure,i.e., tilting) above the engine compartment. Upon deformation then,because of the increase in clearance there is an increase in the amountof the energy that can be absorbed by deformation of the sheet metalbefore bottoming out. One drawback to such hood lifting mechanisms isthat they tend to be irreversible (which makes them best suited for useonly with crash and not with pre-crash sensors), so that such mechanismswill need to be replaced/repaired even if a collision does not in factoccur.

Accordingly, there remains a need in the art for automotive hoodcomponents having improved energy absorbing capabilities. Themeans/mechanisms that produce these energy-absorbing capabilities aredesirably reversible as well.

BRIEF SUMMARY

An exemplary embodiment of a cam lift and reset assembly is disclosed.The assembly includes a cam mounted on a rotatable shaft having a camprofile effective to provide a lifting force to a contacted part thereonupon rotation of the shaft and movement of the cam profile of the camrelative to the contacted part from a rest position to a lift position.The assembly also includes an active material in operative communicationwith the shaft, the active material being operative to change at leastone property of the active material in response to an activation signalso as to effect rotation of the shaft. The assembly further includes areset device in operative communication with the shaft to provide areset force to the contacted part and counter-rotation of the shaft andmovement of the cam profile of the cam relative to the contacted partfrom the lift position to the rest position.

An exemplary embodiment of a process for operating a cam lift and resetassembly that comprises a cam mounted on a rotatable shaft and having acam profile; an active material in operative communication with theshaft; and a reset device in operative communication with the shaft isalso disclosed. The process includes sensing a condition. It alsoincludes activating the active material in response to the sensedcondition to effect rotation of the shaft. The process also includesusing the rotation of the shaft to provide a lifting force to acontacted part thereon and movement of the cam profile of the camrelative to the contacted part. Still further, the process includesraising the contacted part from a rest position to a lift position. Yetfurther, the process includes activating the reset device to effectcounter-rotation of the shaft and using the counter-rotation of theshaft to provide a reset force to the contacted part thereon andmovement of the cam profile of the cam relative to the contacted part.Still further, the process includes lowering the contacted part from thelift position to the rest position.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the invention when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages and details appear, by way of example only,in the following detailed description of embodiments, the detaileddescription referring to the drawings in which:

FIG. 1 is a block diagram showing common elements of hood mechanisms;

FIG. 2 is a schematic representation of a cross-section of a linear rodactive hood lift mechanism in rest and lift positions;

FIG. 3 is a schematic representation of a cross-section of a torsionalrod active hood lift mechanism in rest and lift positions;

FIG. 4 is a schematic representation of a cross-section of a bucklingwire active hood lift mechanism in rest and lift positions;

FIG. 5 is a schematic representation of a cross-section of a bowingouter surface active hood lift mechanism in rest (A) and lift (B)positions;

FIG. 6 is a schematic representation of a cross-section of a springsandwich active hood lift mechanism in rest (A) and lift (B) positions;

FIG. 7 is a schematic representation of a cross-section of a leveractive hood lift mechanism in rest (A) and lift (B) positions:

FIG. 8 is a schematic representation of a cross-section of a wedgeactive hood lift mechanism in rest (A) and lift (B) positions;

FIG. 9 is a schematic representation of a cross-section of a cam activehood lift mechanism in rest (A) and lift (B) positions;

FIG. 10 is a schematic representation of a cross-section of a coilspring passive hood lift mechanism in rest (A) and lift (B) positions;

FIG. 11 is a schematic representation of a cross-section of a tensionedleaf spring passive hood lift mechanism in rest (A) and lift (B)positions;

FIG. 12 is a schematic representation of a cross-section of a centerlatch compressed hood passive hood lift mechanism in rest (A) and lift(B) positions;

FIG. 13 is a schematic representation of a cross-section of an end latchtensioned hood passive hood lift mechanism in rest (A) and lift (B)positions;

FIG. 14 is a schematic representation of a cross section of a cam activehood lift mechanism in accordance with an embodiment of the presentdisclosure;

FIG. 15 is a schematic representation of a perspective view of anexemplary cam active hood lift mechanism in accordance with anotherembodiment of the present disclosure;

FIG. 16 is a schematic representation of a cross section of the camactive hood lift mechanism of FIG. 15 in a lift position;

FIG. 17 is a schematic representation of a cross section of the camactive hood lift mechanism of FIG. 15 in a rest position; and

FIG. 18 illustrates a process flow of exemplary control logic forreversibly and selectively activating an active material based hood liftmechanism;

FIG. 19 is a schematic representation of a perspective view of anexemplary embodiment of a cam active hood lift and reset mechanism inaccordance with another embodiment of the present disclosure;

FIG. 20 is a front view of the mechanism of FIG. 19 in a rest position;

FIG. 21 is a front view of the mechanism of FIG. 19 in a lift position;

FIG. 22 is a front view of a second exemplary embodiment of a cam activehood lift and reset mechanism in accordance with the present disclosurein a rest position;

FIG. 23 is a front view of the mechanism of FIG. 22 in a lift position;

FIG. 24 is a front view of a third exemplary embodiment of a cam activehood lift and reset mechanism in accordance with the present disclosurein a rest position;

FIG. 25 is a front view of the mechanism of FIG. 24 in a lift position;

FIG. 26 is a side view of the mechanism of FIG. 25 in a lift position;and

FIG. 27 is a side view of the mechanism of FIG. 24 in a rest position.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, its application or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

In accordance with an exemplary embodiment of the present invention,methods and hood lift mechanisms for reversibly increasing the energyabsorption capability at appropriate force levels of a vehicle hood aredisclosed herein. In contrast to the prior art, the methods and liftmechanisms disclosed herein advantageously are based on active materialsand provide reversibility. As used herein, the term “hood” is synonymouswith “closure” and generally refers to lids covering an enginecompartment, or a storage compartment, or fuel tank areas as well as tovehicle doors for passenger entry into and out of the vehicle, liftgates, tail gates, cargo hatches, and the like. In addition, for thepurposes of this disclosure, the term hood and/or closure is also meantto include deployable panels such as fenders, bumpers, roofs, and thelike. The term “vehicle body” as used herein generally refers to partsof the vehicle onto which the hood may be fastened and includes, amongothers, bumper support, jams, fender support, chassis, pillars, frameand sub-frame components, and the like. The term “active material” asused herein generally refers to a material that exhibits a change in aproperty such as dimension, shape, shear force, or flexural modulus uponapplication of an activation signal. Suitable active materials include,without limitation, shape memory alloys (SMA), ferromagnetic SMAs, shapememory polymers (SMP), piezoelectric materials, electroactive polymers(EAP), magnetorheological fluids and elastomers (MR), andelectrorheological fluids (ER). Depending on the particular activematerial, the activation signal can take the form of, withoutlimitation, an electric current, a temperature change, a magnetic field,a mechanical loading or stressing, or the like.

Also, as used herein, the terms “first”, “second”, and the like do notdenote any order or importance, but rather are used to distinguish oneelement from another, and the terms “the”, “a”, and “an” do not denote alimitation of quantity, but rather denote the presence of at least oneof the referenced item. Furthermore, all ranges disclosed herein areinclusive of the endpoints and independently combinable.

In one embodiment, a method for reversible and on-demand increase ofenergy absorption capabilities of a hood generally comprises producingan activation signal with an activation device, applying the activationsignal to the active material, and increasing a clearance distancebetween the hood and an underlying component. Producing the activationsignal may comprise sensing an impact event, sensing the imminence of animpact event, manual activation by an occupant, electronic activationthrough a built-in logic control system based on inputs, such as forexample, activation of a vehicle stability enhancement system (VSES),turning on or off the ignition, anti-lock brake activation, and thelike.

In another embodiment, the hood lift mechanism generally comprises anactivation device, and the active material in operative communicationwith the hood, wherein the active material undergoes a property changeresulting in an increased clearance distance between the hood and theunderlying component.

The activation device is operable to selectively apply the activationsignal to the active material. The activation signal provided by theactivation device may include a heat signal, a magnetic signal, anelectrical signal, a pneumatic signal, a mechanical signal, and thelike, and combinations comprising at least one of the foregoing signals,with the particular activation signal dependent on the materials and/orconfiguration of the active material. For example, a magnetic and/or anelectrical signal may be applied for changing the property of the activematerial fabricated from magnetostrictive materials. A heat signal maybe applied for changing the property of the active material fabricatedfrom shape memory alloys and/or shape memory polymers. An electricalsignal may be applied for changing the property of the active materialfabricated from electroactive materials, piezoelectrics, electrostatics,and/or ionic polymer metal composite materials.

Desirably, for direct actuation mechanisms the change in the property ofthe active material remains for the duration of the applied activationsignal. Also desirably, upon discontinuation of the activation signal,the property reverts substantially to its original form prior to thechange. In this manner, reversibility can advantageously occur.

Depending on the particular hood lift mechanism chosen, the activematerial may provide increased clearance distance through a change in ahood shape (i.e., geometry), a hood location, a hood orientation, or acombination comprising at least one of the foregoing changes. Prior tothe active material providing the increased clearance distance, the hoodis said to be in a so-called “rest position”. When the active materialhas provided the increased clearance distance, the hood is said to be ina “lift position” or “lifted position”. The hood may change from therest position to the lift position through active and/or passive meansas will be described in greater detail below.

In some embodiments, the hood may change from the rest position to thelift position through an active hood lift mechanism. Active hood liftmechanisms include direct, composite, and indirect active hood liftmechanisms.

With direct mechanisms, the active material directly acts on the hood toprovide the increased clearance distance. Suitable direct active hoodlift mechanisms include linear rod mechanisms, torsional rod mechanisms,buckling wire mechanisms, and the like.

The active material, in operative communication with the hood, increasesthe energy absorbing capabilities by changing the hood shape, changingthe hood stiffness, changing the stiffness of the mounting hardware,and/or changing the hood orientation through active lifting and/oractive tilting means to provide increased clearance from underlyingengine compartment. The resulting deformation behavior includingstiffness and modulus properties can be altered either globally orlocally.

In one embodiment, the active material changes the shape or orientationof a vehicle hood in response to an activation signal. A device oractuator contains the active material, wherein the active material has afirst shape, dimension, or stiffness and is operative to change to asecond shape, dimension, stiffness, and/or provide a change in shearstrength in response to the activation signal. The device is designed tobe installed in operative communication with the hood.

In another embodiment, a vehicle system contains an impact sensor thatgenerates an impact signal. The system further contains a controllerdisposed to receive the impact signal and a hood impact mitigationdevice that operates upon receiving the activation signal from thecontroller. The active material changes its shape, stiffness or otherphysical property in response to the activation signal. The mitigationdevice, for example, may be a hood lifter.

In various embodiments, the response of the mitigation device to thesignal may be reversible (to prevent damage in the event that an impactdoes not occur) and/or may be tailored both locally and globally to theparticular nature of the impact event. It may also, for example, in thecase of stiffness changes, be unnoticeable or undetectable (fullyreversible), unless an impact occurs, to the vehicle operator. Further,there is minimal interference with vehicle operation. Common elements tothe various embodiments described herein are illustrated in FIG. 1. Suchelements include a sensor 2 plus a controller 4 for triggering theactive material based mechanism 6. It further contains a power source 8and one or more active materials 14 incorporated into the mechanism 6.In a preferred mode of operation, the mechanism is unpowered duringnormal driving and is activated or powered when triggered by an outputsignal from the controller 4 based on input to it from an impact orpre-impact sensor, schematically illustrated by 9 in FIG. 1. Such amechanism would remain activated through the impact event anddeactivated upon the conclusion of the impact event. In an alternativeembodiment, the mechanism would be deactivated upon a timer timing out,which would be useful in the case of a false detect.

For example, FIG. 2 depicts an exemplary linear rod active hood liftmechanism 10 in the rest and lift positions. The hood 12 comprises arotating pivot point 14 at one end. Pivot point 14 provides a means ofattachment for hood 12 to a vehicle body (not shown). A lifting rod 24is disposed on hood 12 on an end opposite to pivot point 14. An activematerial 18 is disposed on lifting rod 24. Connector 22 is coupled toand in operative communication with active material 18 on an endopposite to lifting rod 24. Connector 22 provides a means of attachmentfor active material 18 to an activation device (not shown), which is ata fixed location. A clearance distance 20 is defined as a distancebetween hood 12 and an under hood rigid body component 16, e.g., anengine. In the rest position, clearance distance 20 is at a minimum.

Producing the activation signal with the activation device (not shown)and applying the activation signal to active material 18 effects achange in at least one property of active material 18. When the changein the at least one property is effected, active material 18 exerts alinear pulling force on lifting rod 24, which results in an increasedclearance distance 20 owing to a change in the hood location. Underthese circumstances, hood 12 is no longer in the rest position, but inthe lift position. For example, if the active material is a shape memoryalloy or polymer, the activation signal may comprise a thermal signal,which causes contraction of the shape memory alloy or polymer, resultingin a change in hood location.

Alternatively, multiple lifting rods may be used in parallel to enableboth a change in hood location and orientation.

In another embodiment, lifting rod 24 may substitute for active material18 and is formed from an active material. Alternatively, lifting rod 24may comprise an active material, which optionally is the same activematerial used in active material 18.

FIG. 3 depicts an exemplary torsional rod active hood lift mechanism 50in the rest and lift positions. The hood 12 comprises a rotating pivotpoint 14 at one end. Pivot point 14 provides a means of attachment forhood 12 to a vehicle body (not shown). The rotation of pivot point 14 iscontrolled by a torsional rod (not shown). The torsional rod is coupledto and in operative communication with the active material (not shown).In the rest position, shown in FIG. 2 as dashed hood 12, clearancedistance 20 is at a minimum.

Producing the activation signal with the activation device (not shown)and applying the activation signal to the active material effects achange in the property of the active material. When the change in theproperty is effected, the active material exerts a rotational force onthe torsional rod, which results in an increased clearance distance 20,owing to a change in the hood location. Under these circumstances, hood12 is no longer in the rest position, but in the lift position, shown inFIG. 2 as shaded hood 12. Optionally, the torsional rod is formed of theactive material.

FIG. 4 depicts an exemplary buckling wire active hood lift mechanism 100in the rest and lift positions. The hood 12 comprises a rotating pivotpoint 14 at one end, which provides a means of attachment for hood 12 toa vehicle body (not shown). Active material 18 is fixedly attached tohood 12 at the same end as pivot point 14. At an end opposite pivotpoint 14, active material 18 is coupled to and in operativecommunication with connector 112. Connector 112 provides a means ofattachment for active material 18 to hood 12 and to an activation device(not shown). A predetermined buckling point 114 is interposed at aposition on hood 12 between pivot point 14 and connector 112. In therest position, shown in FIG. 3 as dashed hood 12, clearance distance 20is at a minimum.

Producing the activation signal with the activation device (not shown)and applying the activation signal to active material 18 effects achange in at least one property of active material 18. When the changein the property is effected, active material 18 exerts a linear pullingforce on hood 12, resulting in hood 12 buckling at predeterminedbuckling point 114 and an increased clearance distance 20. Under thesecircumstances, hood 12 is no longer in the rest position, but in thelift position owing to a change in the hood geometry and orientation,shown in FIG. 3 as shaded hood 12. Alternatively, buckling can bedistributed along the length of the hood.

In another embodiment, active material 18 may be fixedly attached tohood 12 at an end opposite to pivot point 14; and coupled to and inoperative communication with connector 112 at the same end as pivotpoint 14.

With composite mechanisms, the active material 18 is embedded within thehood 12. Suitable composite active hood lift mechanisms include bowingouter surface mechanisms, spring sandwich mechanisms, and the like.

FIG. 5 depicts an exemplary bowing outer surface active hood liftmechanism 150 in rest (5A) and lift (5B) positions. The hood 12comprises an outer portion 164 and an inner portion 166 as well as arotating pivot point 14 at one end. Pivot point 14 provides a means ofattachment for hood 12 to a vehicle body (not shown). Active material 18is embedded within outer portion 164 of hood 12. Active material 18 isfixedly attached to hood 12 at the same end as pivot point 14. At an endopposite pivot point 14, active material 18 is coupled to and inoperative communication with connector 162. Connector 162 provides ameans of attachment for active material 18 to outer portion 164 of hood12 and to an activation device (not shown). In the rest position shownin FIG. 5A, clearance distance 20 is at a minimum.

Producing the activation signal with the activation device (not shown)and applying the activation signal to active material 18 effects achange in the property of active material 18. When the change in theproperty is effected, active material 18 exerts a pulling force,resulting in outer portion 164 of hood 12 bowing away from under hoodrigid body 16 and an increased clearance distance 20. Under thesecircumstances, hood 12 is no longer in the rest position, but in thelift position shown in FIG. 5B, owing to a change in the hood geometryand/or orientation. For example, if the active material is a shapememory alloy, the activation signal may comprise a thermal signal, whichcauses contraction of the shape memory alloy, resulting in a change inhood geometry and/or orientation.

In another embodiment, both the outer portion 164 and inner portion 166of hood 12 bow away from under hood rigid body 16 when the change in theat least one property is effected. Alternatively, hood 12 may comprise asingle portion, which bows away from under hood rigid body 16 when thechange in the at least one property is effected.

FIG. 6 depicts an exemplary spring sandwich active hood lift mechanism200 in rest (6A) and lift (6B) positions. The hood 12 comprises an outerportion 212 and an inner portion 214, wherein one or more springs 204are interposed. The one or more springs 204 exert a pushing force onouter portion 212 of hood 12 away from inner portion 214 of hood 12. Theone or more springs 204 are compressed by the active material (notshown), which is embedded in hood 12. In the rest position shown in FIG.6A, clearance distance 20 is at a minimum

Producing the activation signal with the activation device (not shown)and applying the activation signal to the active material effects achange in at least one property of the active material. When the changein the at least one property is effected, the active material releasesthe one or more springs 204, resulting in outer portion 212 of hood 12being pushed away from under hood rigid body 16 and an increasedclearance distance 20. Under these circumstances, hood 12 is no longerin the rest position, but in the lift position shown in FIG. 6B, owingto a change in the hood location.

In another embodiment, the one or more springs 204 are formed from anactive material. Alternatively, the one or more springs 204 may comprisean active material, which optionally is the same active material that isembedded in the hood 12, if present.

With indirect mechanisms, the active material indirectly acts on thehood via a leveraging material. Suitable indirect active hood liftmechanisms include lever mechanisms, wedge mechanisms, cam mechanisms,and the like.

FIG. 7 depicts an exemplary lever active hood lift mechanism 250 in rest(7A) and lift (7B) positions. The hood 12 comprises a rotating pivotpoint 14 at one end. Pivot point 14 provides a means of attachment forhood 12 to a vehicle body (not shown). A lever 264 is disposed on hood12 on an end opposite to pivot point 14. On an end opposite to hood 12,active material 18 is disposed on lever 264. Lever 264 may rotate aboutlever pivot point 266. Connector 262 is coupled to and in operativecommunication with active material 18 on an end opposite to lever 264.Connector 262 provides a means of attachment for active material 18 toan activation device (not shown). In the rest position shown in FIG. 7A,clearance distance 20 is at a minimum.

Producing the activation signal with the activation device (not shown)and applying the activation signal to active material 18 effects achange in at least one property of active material 18. When the changein the at least one property is effected, active material 18 exerts alinear pulling force on lever 264, which rotates about lever pivot point266 to increase clearance distance 20 and changes the hood location.Under these circumstances, hood 12 is no longer in the rest position,but in the lift position shown in FIG. 7B.

FIG. 8 depicts an exemplary wedge active hood lift mechanism 300 in rest(8A) and lift (8B) positions. The hood 12 comprises a rotating pivotpoint 14 at one end. Pivot point 14 provides a means of attachment forhood 12 to a vehicle body (not shown). A wedge 314 is disposed inproximity to hood 12 on an end opposite to pivot point 304. Activematerial 18 is fixedly attached to wedge 314. At an end opposite wedge314, and the same as pivot point 14, active material 18 is coupled toand in operative communication with connector 312. Connector 312provides a means of attachment for active material 18 to hood 12 and toan activation device (not shown). In the rest position shown in FIG. 8A,clearance distance 20 is at a minimum.

Producing the activation signal with the activation device (not shown)and applying the activation signal to active material 18 effects achange in at least one property of active material 18. When the changein the at least one property is effected, active material 18 exerts alinear pulling force on wedge 314 towards connector 312, resulting in anincreased clearance distance 20. Under these circumstances, hood 12 isno longer in the rest position, but in the lift position shown in FIG.8B, owing to a change in the hood location.

In another embodiment, active material 18 may be fixedly attached tohood 12 at an end opposite to wedge 314; and coupled to and in operativecommunication with connector 312 at wedge 314.

FIG. 9 depicts an exemplary cam active hood lift mechanism 350 in rest(9A) and lift (9B) positions. The hood 12 comprises a rotating pivotpoint 14 at one end. Pivot point 14 provides a means of attachment forhood 12 to a vehicle body (not shown). A cam 364 is disposed on hood 12on an end opposite to pivot point 14. On an end opposite to hood 12,active material 18 is coupled and in operative communication with cam364 at cam pivot point 366. Cam 364 may rotate about cam pivot point366. Connector 362 is coupled to and in operative communication withactive material 18 on an end opposite to cam 364. Connector 362 providesa means of attachment for active material 18 to an activation device(not shown). In the rest position shown in FIG. 9A, clearance distance20 is at a minimum.

Producing the activation signal with the activation device (not shown)and applying the activation signal to active material 18 effects achange in at least one property of active material 18. When the changein the at least one property is effected, active material 18 exerts alinear pulling force on cam 364, which rotates about cam pivot point 366to increase clearance distance 20 and changes the hood location. Underthese circumstances, hood 12 is no longer in the rest position, but inthe lift position, shown in FIG. 9B.

In another embodiment, the cam could be rotated by a torsional dowelmade of SMA, for example, to lift the hood when the SMA is heated. Atorsional spring could reset the cam when the SMA is cooled. The camprofile could be designed with a flat top or a notch so that the hoodcould be held in the lifted position.

In some embodiments, a passive hood lift mechanism may be employed,wherein a stored energy is taken advantage of to cause the change fromthe rest position to the lift position. Passive hood lift mechanismsinclude external and in-hood passive hood lift mechanisms.

With external mechanisms, the active material 18 releases energy that isstored in an external device such as for example a spring. Suitableexternal passive hood lift mechanisms include coil spring mechanisms,leaf spring mechanisms, and the like.

FIG. 10 depicts an exemplary coil spring passive hood lift mechanism 400in rest (10A) and lift (10B) positions. The hood 12 comprises a rotatingpivot point 14 at one end. Pivot point 14 provides a means of attachmentfor hood 12 to a vehicle body (not shown). One or more coil springs 414are disposed on hood 12 on an end opposite to pivot point 404. On an endopposite hood 12, the one or more coil springs 414 are disposed on thevehicle body. The one or more coil springs 414 exert a pushing force onhood 12 away from the vehicle body. On an end opposite hood 12, and thesame end as the vehicle body, active material 18 is coupled to and inoperative communication with the one or more coil springs 414. The oneor more coil springs 414 are compressed by the active material (notshown). Connector 412 is coupled to and in operative communication withactive material 18 on an end opposite to the one or more coil springs414. Connector 412 provides a means of attachment for active material 18to an activation device (not shown). In the rest position shown in FIG.10A, clearance distance 20 is at a minimum.

Producing the activation signal with the activation device (not shown)and applying the activation signal to active material 18 effects achange in at least one property of active material 18. When the changein the at least one property is effected, active material 18 releasesthe one or more coil springs 414 to an uncompressed position, resultingin hood 12 being pushed away from under hood rigid body 16 and anincreased clearance distance 20. Under these circumstances, hood 12 isno longer in the rest position, but in the lift position shown in FIG.10B, owing to a change in the hood location.

In another embodiment, the one or more coil springs 414 may be formedfrom an active material the same as or different from active material18, if present.

FIG. 11 depicts an exemplary leaf spring passive hood lift mechanism 450in rest (11A) and lift (11B) positions. The hood 12 comprises a rotatingpivot point 14 at one end. Pivot point 14 provides a means of attachmentfor hood 12 to a vehicle body (not shown). One or more leaf springs 464are fixedly attached on one end to hood 12 at the same end as pivotpoint 14. The one or more leaf springs 464 are held in tension againsthood 12 at an end opposite pivot point 14. Active material 18 is coupledto and in operative communication with the one or more leaf springs 464at the end opposite pivot point 14. Active material 18 provides a meansof attachment for the one or more leaf springs 464 to hood 12. At an endopposite the one or more leaf springs 464, active material 18 is coupledto and in operative communication with connector 462. Connector 462provides a means of attachment for active material 18 to an activationdevice (not shown). In the rest position shown in FIG. 11A, clearancedistance 20 is at a minimum.

Producing the activation signal with the activation device (not shown)and applying the activation signal to active material 18 effects achange in at least one property of active material 18. When the changein the at least one property is effected, active material 18 releasesthe one or more leaf springs 464 from hood 12, resulting in hood 12bowing away from under hood rigid body 16 and an increased clearancedistance 20. Under these circumstances, hood 12 is no longer in the restposition, but in the lift position shown in FIG. 11B, owing to a changein the hood geometry and location. Optionally, the leaf spring is formedof the active material.

With in-hood mechanisms, the active material 18 releases energy that isstored in a pre-compression configuration of the hood 12. Suitablein-hood passive hood lift mechanisms include center latch mechanisms,end latch mechanisms, and the like. Optionally, the latch can be at alocation apart from the actuator location, e.g., a rotary latch at thefront hinge.

FIG. 12 depicts an exemplary center latch passive hood lift mechanism500 in rest (12A) and lift (12B) positions. The hood 12 comprises anouter portion 514 and an inner portion 516 as well as a rotating pivotpoint 14 at one end. Pivot point 14 provides a means of attachment forhood 12 to a vehicle body (not shown). Active material 18 is interposedat any position on hood 12 between pivot point 14 and an end opposite topivot point 14. Active material 18 is coupled to and in operativecommunication with hood 12. Active material 18 provides a means ofattachment for outer portion 514 and inner portion 516 of hood 12. At anend opposite hood 12, active material 18 is coupled to and in operativecommunication with a connector (not shown). The connector provides ameans of attachment for active material 18 to an activation device (notshown). In the rest position, shown in FIG. 12A, clearance distance 20is at a minimum.

Producing the activation signal with the activation device (not shown)and applying the activation signal to active material 18 effects achange in the property of active material 18. When the change in theproperty is effected, the release of outer portion 514 of hood 12 frominner portion 516 of hood 12 is effected, resulting in outer portion 514of hood 12 bowing away from under hood rigid body 16 and an increasedclearance distance 20. Under these circumstances, hood 12 is no longerin the rest position, but in the lift position shown in FIG. 12B, owingto a change in the hood geometry and/or orientation.

FIG. 13 depicts an exemplary end latch passive hood lift mechanism 550in rest (13A) and lift (13B) positions. The hood 12 comprises an outerportion 564 and an inner portion 566 as well as a rotating pivot point14 at one end. Pivot point 14 provides a means of attachment for hood 12to a vehicle body (not shown). Active material 18 is disposed on hood 12at an end opposite to pivot point 14. Active material 18 is coupled toand in operative communication with hood 12. Active material 18 providesa means of attachment for outer portion 564 and inner portion 566 ofhood 12. At an end opposite hood 12, active material 18 is coupled toand in operative communication with a connector (not shown). Theconnector provides a means of attachment for active material 18 to anactivation device (not shown). In the rest position, shown in FIG. 13A,clearance distance 20 is at a minimum.

Producing the activation signal with the activation device (not shown)and applying the activation signal to active material 18 effects achange in at least one property of active material 18. When the changein the at least one property is effected, the release of outer portion564 of hood 12 from inner portion 566 of hood 12 is effected, resultingin outer portion 564 of hood 12 bowing away from under hood rigid body16 and an increased clearance distance 20. Under these circumstances,hood 12 is no longer in the rest position, but in the lift positionshown in FIG. 13B, owing to a change in the hood geometry and/ororientation. Alternatively, the hood can be configured such that theentire hood panel bows to provide the increased clearance.

FIG. 14 provides a detailed schematic illustration of an exemplary camlifter, which employs active materials. Advantageously, the cam liftmechanism, in general, provides a relatively simple mechanism forselectively lifting the hood. Reset can be occur by simply reversing camrotation, which can be spring driven, manual actuated, or actuated usingactive materials. The cam lifter provides a tunable force and motionresponse based on the particular cam design employed. The presentdisclosure is not intended to be limited to any particular cam shape andthe cam shape shown in FIG. 14 is intended to be exemplary. In addition,it should be noted that the cam lift can be independently positioned inoperative communication with the hood or may be integrated with anexisting hinge mechanism depending ton the desired application.

As shown FIG. 14, a cam lift assembly 600 includes an active material602 configured to selectively rotate a cam 604. By way of example, theactive material can be a wire 603 or band formed of shape memory alloyin the form of a torsional spring 607 that is in operative communicationwith a rod 606, such as by being fixed to a pin attaching. The torsionalspring can be disposed within shaft or externally. The cam 604 ispositioned in operative communication with the rod 606 such thatrotation of the torsional rod 606 effects rotation of the cam 604. In apreferred embodiment, at least two cam mechanisms 600 are positioned ateach end of the pivot point of the hood so as to provide substantiallyuniform lifting of the hood upon activation. During operation, the liftassembly 600 is activated as the SMA wire is heated, causing the wire tocontract and rotate the rod as illustrated by arrow 608. The rod 606,being directly connected to the lifting cam, rotates the cam and liftsthe hood 12 from a resting position to a raised position as indicated byarrow 610. The cam profile could be designed with a flat 609 on the topor to fit into a notch so the hood 12 would be held in the liftedposition. Again, the cam shape is not intended to be limited and willgenerally depend on the intended application and desired liftingparameters. Generally, the desired hood motion will be considered in thedesign of the cam shape. After the SMA wire cools, rotating the rod witha reset device 601 or mechanism such as an SMA reset device, a biasspring or manually turning back the cam by hand would obtain a systemreset. An SMA reset device may include an SMA torsion spring 611comprising a second SMA wire 612 wound in the opposite direction as thatof torsion spring 607. During operation, the reset device 600 orassembly is activated as the second SMA wire 612 is heated, causing thewire to contract and counter-rotate the rod as illustrated by arrow 613.

FIGS. 15-17 illustrates various views of a cam lift assembly 650 inaccordance with one embodiment. The cam lift assembly 650 includes a cam652 mounted to an axle 654. The axle 654 includes a torsional springform of SMA having one end external to the axle and attached to astationary member 655. Framing members 656, which are mounted to thevehicle and positioned to provide the cam assembly 650 a lifting force acontacted part, such as on a hood 12, rotatably supports the axle 654.The movement of the cam profile 663 relative to the hood 12 provides thelifting force for hood 12. The hood, e.g., 12 as previously shown, canbe optionally attached to the cam lift assembly via post 660. In thisoptional embodiment, the post 660 is engaged with a slot opening 662 inthe cam 652 having a pathway such that rotation of the cam 652 andmovement of the cam profile 663′ relative to the contacted part (post660) results in selectively lifting the hood from a vehicle frame thatsupports the hood or vice versa. The end of slot opening 662 comprises adetent 661 for cam 652 that is adapted to engage a surface of thecontacted part, namely post 660, so as to prevent further rotation ofthe shaft. An activation device (not shown) is coupled to the shapememory alloy. FIGS. 16 and 17 illustrate the cam in a lift position anda rest position.

In FIG. 18, an exemplary control logic flow chart 700 is illustratedusing the hood lift actuator. As noted, the response of the device tothe signal may be reversible (to prevent damage in the event that animpact does not occur) and/or may be tailored both locally and globallyto the particular nature of the impact event. It may also, for example,in the case of stiffness changes, be unnoticeable or undetectable (fullyreversible), unless an impact occurs, to the vehicle operator. Further,there is minimal interference with vehicle operation. Using hood liftactuator 600 as an example, at step 702, the vehicle is started andenables the hood lift actuator to be selectively actuated if it isdetermined a condition 706 is detected, (e.g., an impact event, apre-impact event, and the like). Upon detecting a condition, the axle654 of the hood lift actuator rotates as a function of the activematerial and the cam 652 provides a lifting force to the hood 12,thereby raising the hood. The hood is maintained 710 in this positionuntil the condition is no longer detected. In this particularembodiment, an activation signal to the active material may or may notbe discontinued depending on the configuration of the actuator. To resetthe hood to its original position, the activation signal that providedthe rotation of the axle to the lift position is discontinued and a biasspring, active material or some other mechanism restores the hood to itsoriginal position as described herein, i.e., the cam is rotated. Shapememory alloy wires are thermally activated such that the pin assembly624 clears and engages the second member so as to retain the compressiveforces in springs 606 as noted in step 714. Once reset, the actuator 600can be used to detect a condition.

In the event a crash is not sensed as noted in step 716, the actuatorcan be turned off and the stored energy of the compression spring 606released as in step 718. Dissipation of the stored energy can beeffected by selectively retracting the pin assembly 626 and the vehicleturned off. In one mode of operation, the mechanism is unpowered duringnormal driving and is activated or powered when triggered by an outputsignal from the controller based on input to it from an impact orpre-impact sensor, schematically illustrated by 9 in FIG. 1. Such amechanism would remain activated through the impact event but thenautomatically be deactivated upon the conclusion of the impact. In analternative embodiment, the mechanism would be deactivated upon a timertiming out, which would be useful in the case of a false detect.Alternatively, as shown in FIG. 19, the control logic can be configuredto permit servicing as indicated by step 720.

FIGS. 19-21 illustrates various views of a cam lift assembly and resetassembly 670 in accordance with one embodiment. The cam lift assemblyincludes a a cam 652 mounted on a rotatable shaft or axle 654 having acam profile 663 effective to provide a lifting force to a contacted partthereon, such as a hood 12, upon rotation of the axle 654 and movementof the cam profile 663 of the cam 652 relative to the contacted partfrom a rest position 13 to a lift position 15. The cam lift assembly 650also includes an active material in operative communication with theaxle 654. The active material being operative to change at least oneproperty of the active material in response to an activation signal soas to effect rotation of the axle 654.

The cam lift assembly 650 includes a cam 652 mounted to a rotatable axle654. The axle 654 includes at least one torsional spring 664 formed ofan active material, such as an SMA. In the embodiment of FIGS. 19-21, aplurality of torsional springs 664 formed of SMA are provided in theform of a pair of torsional springs 664 placed on opposing sides of thecam 652. This arrangement is useful for balancing the rotational forcesapplied by torsional springs 664 along axle 654 on either side of cam652 during operation. Each torsional spring 664 is formed by attachingan intermediate portion 665 (e.g., a central portion) of an SMA wire667, or a plurality of SMA wires, to a spool 666 that is fixed to androtatable with axle 654. Spool 666 may also be joined to cam 652 by, forexample, either abutting (e.g., using two separate spools 666) orextending through (e.g., a single spool 666) and being joined to cam652, such as by a weld joint, braze joint or adhesive joint or the like.By attaching intermediate portion 665 of wire 667, the wire is dividedinto two sections. A first section 673 extends from intermediate portion665 to a first end 669. A second section 675 extends from intermediateportion 665 to a second end 671. Each of first section 673 and secondsection 675 of wire 667 is wrapped radially around the spool 666 in thesame direction and axially away from the other. First end 669 isattached to a first portion, such as terminal 677, of stationary member655 and second end 671 is attached to a second portion of stationarymember 655, such as terminal 679. First portion, such as first terminal677, and second portion, such as second terminal 679 may be spaced fromone another along stationary member. Torsional springs 664 may, forexample, be activated by resistance heating of the wire 667 to cause theSMA to shrink, thereby causing the wire to act on the spool 666 to causeboth the spool 666 and axle 654 to which it is fixed to rotate withinopposing frame members 656 located on opposing sides of cam 652. Uponactivation, as the axle 654 rotates, the cam 652 also rotates from theinitial or rest (or reset) position (FIG. 20) to the lifted position(FIG. 21). The spool 666 can be fitted over the axle 665 and sized toprovide a predetermined diameter of both the spool 666 and torsionalsprings 664 provided on the spool 666. It will be recognized that axle654 may also be designed to provide a plurality of different diameters,including the diameter of spool 666 so that the use of a separate spoolis not required. The intermediate portions 665 of wires 667 may beattached in any suitable manner or with the use of various attachmentdevices, such as pin 668, or other fasteners, or by joining the wire tothe pin 668 (or directly to spool 666) with various joints, such as aweld joint, braze joint or adhesive joint or the like. It will also beunderstood that rather than a single wire 667, the first section 669 andsecond section 671 may also comprise two separate wires in accordancewith the invention. Framing members 656 may be mounted to a vehicle andpositioned to provide the cam assembly 650 a lifting force against acontacted part, such as on a hood 12, as described herein. The movementof the cam profile 663 relative to the hood 12 provides the liftingforce for hood 12 to lift the hood 12 from an initial (or reset)position 13 to a lifted position 15. As illustrated in FIG. 15, the hood12, as previously shown, can be optionally attached to the cam liftassembly 650 via post 660. In this optional embodiment, the post 660 isengaged with a slot opening 662 in the cam 652 having a pathway suchthat rotation of the cam 652 and movement of the cam profile 663′relative to the contacted part (post 660) results in selectively liftingthe hood from a vehicle frame that supports the hood or vice versa. Theend of slot opening 662 comprises a detent 661 for cam 652 that isadapted to engage a surface of the contacted part, namely post 660, soas to prevent further rotation of the shaft. An activation device (notshown) may be provided to activate the SMA wires 667, such as acontroller that is configured to supply power to them to produce I²R(resistance) heating sufficient to cause a phase transformation andshrinking of the wires as described herein.

The hood lift mechanisms shown are exemplary only and are not intendedto be limited to any particular shape, size, configuration, materialcomposition, or the like. Although the hood lift mechanisms describedcomprise a pivot point on one end of the hood, other embodiments includemultiple pivot points on one or more than one end of the hood 12 toenable lifting on any end based on necessity of increased energyabsorption on those ends at a given point. One hood lift mechanism maybe implemented so as to provide a single discrete means of providingincreased clearance or energy absorption; or more than one liftmechanism of one or more types may be implemented to provide multiplemeans for increased clearance or increased energy absorption. In otherembodiments, the active materials may be substituted by active materialbased latches, wherein the active materials effect engagement anddisengagement of the latches.

The lift mechanisms or assemblies described herein, such as cam liftassembly 650, may also be combined with a reset mechanism or assembly.These reset assemblies include reset devices that may be active, suchthat they themselves produce the energy needed to reset the cam liftassembly, or they be passive, such that they passively store energyneeded to reset the cam lift mechanism from the movement of the cam liftassembly. The reset device is in operative communication with the shaftor axle 654 to provide a reset force to the contacted part, such as avehicle hood 12, and counter-rotation of the axle 654 and movement ofthe cam profile 663 of the cam 652 relative to the contacted part fromthe lift position 15 to the rest (or reset) position 13.

One exemplary embodiment of an active reset assembly that includes areset device 670 is shown in FIGS. 19-21. The reset device 670 issimilar in construction to the lift assembly 650, but is configured toprovide an opposite or counter-rotation of the axle 654 and cam 656 toreturn them to the rest (or reset) position 13. The reset device 670includes at least one torsional spring 676 formed of an active material,such as an SMA. In the embodiment of FIGS. 19-21, a plurality oftorsional springs 676 formed of SMA are provided in the form of a pairof torsional springs 676 placed on opposing sides of the cam 652. Thisarrangement is useful for balancing the rotational forces applied bytorsional springs 676 along axle 654 on either side of cam 652 duringoperation. Each torsional spring 676 is formed by attaching anintermediate portion 674 (e.g., a central portion) of an SMA wire 678,or a plurality of SMA wires, to an end of rotatable axle 654 (or a spool(not shown). By attaching intermediate portion 674 of wire 678, the wireis divided into two sections. A first section 680 extends fromintermediate portion 674 to a first end 681. A second section 682extends from intermediate portion 674 to a second end 683. Each of firstsection 680 and second section 682 of wire 678 is wrapped radiallyaround the spool axle 654 in the same direction (a direction oppositethat of wires 667) and axially away from the other. First end 681 isattached to a first portion, such as first terminal 684, of stationarymember 685, and second end 683 is attached to a second portion ofstationary member 685, such as second terminal 686. First portion, suchas first terminal 684, and second portion, such as second terminal 686may be spaced from one another along stationary member 685. Torsionalsprings 676 may, for example, be activated by resistance heating of thewire 678 to cause the SMA to shrink, thereby causing the wire to act onthe axle 654 to cause the axle 654 to counter-rotate. Upon activation,as the axle 654 counter-rotates, the cam 652 also counter-rotates fromthe lifted position (FIG. 21) to the rest (or reset) position (FIG. 20).The axle 654 and sized to provide a predetermined diameter of both theaxle 654 and torsional springs 676 provided on the axle 654. It will berecognized that axle 654 may also be designed to provide a plurality ofdifferent diameters, including the diameter of the end portions on whichtorsional springs 676 are placed. The intermediate portions 674 of wires678 may be attached in any suitable manner or with the use of variousattachment devices, such as pin 672, or other fasteners, or by joiningthe wire to the pin 672 (or directly to axle 654) with various joints,such as a weld joint, braze joint or adhesive joint or the like. It willalso be understood that rather than a single wire 678, the first section680 and second section 682 may also comprise two separate wires inaccordance with the invention. Framing members 656 may be mounted to avehicle and positioned to provide the reset device 670 a reset forceagainst a contacted part, such as on a hood 12, as described herein. Themovement of the cam profile 663 relative to the hood 12 provides thereset force for lowering hood 12 to lower the hood 12 from a liftposition 15 to a rest or reset position 13. As illustrated in FIG. 15,the hood 12, as previously shown, can be optionally attached to the camlift assembly 650 via post 660. In this optional embodiment, the post660 is engaged with a slot opening 662 in the cam 652 having a pathwaysuch that rotation of the cam 652 and movement of the cam profile 663′relative to the contacted part (post 660) results in selectivelylowering or resetting the hood 12. An activation device (not shown) maybe provided to activate the SMA wires 678, such as a controller that isconfigured to supply power to them to produce I²R (resistance) heatingsufficient to cause a phase transformation and shrinking of the wires asdescribed herein.

Another exemplary embodiment of a cam lift and reset assembly isillustrated in FIGS. 22 and 23. This assembly includes cam lift device650 as described above combined with a passive reset device 690 thatincludes a torsional spring 692 comprising a coil spring 694 disposed onan end of axle 654 and engaged on one end 696 to axle 654 or to a pin698 disposed on axle 654, and on the other end 700 engaged to framingmember 656. Reset device may also include a plurality of torsionalsprings 692, including a pair of coil springs 694 located on oppositeends of axle 654. During activation and operation of cam lift device 650to move cam 652 to the lift position 15 (FIG. 23), the torsional spring692 stores energy by winding up coil spring 694. Upon deactivation ofcam lift 650, the SMA wires 667 cool and the energy in coil spring 694counter-rotates axle 654 and cam 652, thereby resetting the contactedpart, such as hood 12, to the rest or reset position 13.

Yet another exemplary embodiment of a cam lift and reset assembly isillustrated in FIGS. 24-27. This assembly includes cam lift device 650as described above combined with a passive reset device 710 thatincludes a linear coil spring 712. Linear coil spring 712 may include aplurality of linear coil springs 712, including the pair of linear coilsprings 712 that each extend from and engage framing member 656, such asfrom projecting arm 714 and including pin 716, and cam 652, includingpin 718. During activation and operation of cam lift device 650 to movecam 652 to the lift position 15 (FIGS. 25 and 26), the linear coilspring 712 stores energy by axially stretching the coil spring 712. Upondeactivation of cam lift 650 (FIGS. 27-28), the SMA wires 667 cool andthe energy in coil spring 712 counter-rotates cam 652 and axle 654,thereby resetting the contacted part, such as hood 12, to the rest orreset position 13.

As previously described, suitable active materials include, withoutlimitation, shape memory alloys (SMA), shape memory polymers (SMP),piezoelectric materials, electro active polymers (EAP), ferromagneticmaterials, magnetorheological fluids and elastomers (MR) andelectrorheological fluids (ER).

Suitable shape memory alloys can exhibit a one-way shape memory effect,an intrinsic two-way effect, or an extrinsic two-way shape memory effectdepending on the alloy composition and processing history. The twophases that occur in shape memory alloys are often referred to asmartensite and austenite phases. The martensite phase is a relativelysoft and easily deformable phase of the shape memory alloys, whichgenerally exists at lower temperatures. The austenite phase, thestronger phase of shape memory alloys, occurs at higher temperatures.Shape memory materials formed from shape memory alloy compositions thatexhibit one-way shape memory effects do not automatically reform, anddepending on the shape memory material design, will likely require anexternal mechanical force to reform the shape orientation that waspreviously exhibited. Shape memory materials that exhibit an intrinsicshape memory effect are fabricated from a shape memory alloy compositionthat will automatically reform themselves.

The temperature at which the shape memory alloy remembers its hightemperature form when heated can be adjusted by slight changes in thecomposition of the alloy and through heat treatment. In nickel-titaniumshape memory alloys, for example, it can be changed from above about100° C. to below about −100° C. The shape recovery process occurs over arange of just a few degrees and the start or finish of thetransformation can be controlled to within a degree or two depending onthe desired application and alloy composition. The mechanical propertiesof the shape memory alloy vary greatly over the temperature rangespanning their transformation, typically providing the shape memorymaterial with shape memory effects as well as high damping capacity. Theinherent high damping capacity of the shape memory alloys can be used tofurther increase the energy absorbing properties.

Suitable shape memory alloy materials include without limitationnickel-titanium based alloys, indium-titanium based alloys,nickel-aluminum based alloys, nickel-gallium based alloys, copper basedalloys (e.g., copper-zinc alloys, copper-aluminum alloys, copper-gold,and copper-tin alloys), gold-cadmium based alloys, silver-cadmium basedalloys, indium-cadmium based alloys, manganese-copper based alloys,iron-platinum based alloys, iron-platinum based alloys, iron-palladiumbased alloys, and the like. The alloys can be binary, ternary, or anyhigher order so long as the alloy composition exhibits a shape memoryeffect, e.g., change in shape orientation, damping capacity, and thelike. For example, a nickel-titanium based alloy is commerciallyavailable under the trademark NITINOL from Shape Memory Applications,Inc.

Other suitable active materials are shape memory polymers. Similar tothe behavior of a shape memory alloy, when the temperature is raisedthrough its transition temperature, the shape memory polymer alsoundergoes a change in shape orientation. Dissimilar to SMAs, raising thetemperature through the transition temperature causes a substantial dropin modulus. While SMAs are well suited as actuators, SMPs are bettersuited as “reverse” actuators. That is, by undergoing a large drop inmodulus by heating the SMP past the transition temperature, release ofstored energy blocked by the SMP in its low temperature high modulusform can occur. To set the permanent shape of the shape memory polymer,the polymer must be at about or above the Tg or melting point of thehard segment of the polymer. “Segment” refers to a block or sequence ofpolymer forming part of the shape memory polymer. The shape memorypolymers are shaped at the temperature with an applied force followed bycooling to set the permanent shape. The temperature necessary to set thepermanent shape is preferably between about 100° C. to about 300° C.Setting the temporary shape of the shape memory polymer requires theshape memory polymer material to be brought to a temperature at or abovethe Tg or transition temperature of the soft segment, but below the Tgor melting point of the hard segment. At the soft segment transitiontemperature (also termed “first transition temperature”), the temporaryshape of the shape memory polymer is set followed by cooling of theshape memory polymer to lock in the temporary shape. The temporary shapeis maintained as long as it remains below the soft segment transitiontemperature. The permanent shape is regained when the shape memorypolymer fibers are once again brought to or above the transitiontemperature of the soft segment. Repeating the heating, shaping, andcooling steps can reset the temporary shape. The soft segment transitiontemperature can be chosen for a particular application by modifying thestructure and composition of the polymer. Transition temperatures of thesoft segment range from about −63° C. to above about 120° C.

Shape memory polymers may contain more than two transition temperatures.A shape memory polymer composition comprising a hard segment and twosoft segments can have three transition temperatures: the highesttransition temperature for the hard segment and a transition temperaturefor each soft segment.

Most shape memory polymers exhibit a “one-way” effect, wherein the shapememory polymer exhibits one permanent shape. Upon heating the shapememory polymer above the first transition temperature, the permanentshape is achieved and the shape will not revert back to the temporaryshape without the use of outside forces. As an alternative, some shapememory polymer compositions can be prepared to exhibit a “two-way”effect. These systems consist of at least two polymer components. Forexample, one component could be a first cross-linked polymer while theother component is a different cross-linked polymer. The components arecombined by layer techniques, or are interpenetrating networks, whereintwo components are cross-linked but not to each other. By changing thetemperature, the shape memory polymer changes its shape in the directionof the first permanent shape of the second permanent shape. Each of thepermanent shapes belongs to one component of the shape memory polymer.The two permanent shapes are always in equilibrium between both shapes.The temperature dependence of the shape is caused by the fact that themechanical properties of one component (“component A”) are almostindependent from the temperature in the temperature interval ofinterest. The mechanical properties of the other component (“componentB”) depend on the temperature. In one embodiment, component B becomesstronger at low temperatures compared to component A, while component Ais stronger at high temperatures and determines the actual shape. Atwo-way memory device can be prepared by setting the permanent shape ofcomponent A (“first permanent shape”); deforming the device into thepermanent shape of component B (“second permanent shape”) and fixing thepermanent shape of component B while applying a stress to the component.

Similar to the shape memory alloy materials, the shape memory polymerscan be configured in many different forms and shapes. The temperatureneeded for permanent shape recovery can be set at any temperaturebetween about −63° C. and about 120° C. or above. Engineering thecomposition and structure of the polymer itself can allow for the choiceof a particular temperature for a desired application. A preferredtemperature for shape recovery is greater than or equal to about −30°C., more preferably greater than or equal to about 0° C., and mostpreferably a temperature greater than or equal to about 50° C. Also, apreferred temperature for shape recovery is less than or equal to about120° C., more preferably less than or equal to about 90° C., and mostpreferably less than or equal to about 70° C.

Suitable shape memory polymers include thermoplastics, thermosets,interpenetrating networks, semi-interpenetrating networks, or mixednetworks. The polymers can be a single polymer or a blend of polymers.The polymers can be linear or branched thermoplastic elastomers withside chains or dendritic structural elements. Suitable polymercomponents to form a shape memory polymer include, but are not limitedto, polyphosphazenes, poly(vinyl alcohols), polyamides, polyesteramides, poly(amino acid)s, polyanhydrides, polycarbonates,polyacrylates, polyalkylenes, polyacrylamides, polyalkylene glycols,polyalkylene oxides, polyalkylene terephthalates, polyortho esters,polyvinyl ethers, polyvinyl esters, polyvinyl halides, polyesters,polylactides, polyglycolides, polysiloxanes, polyurethanes, polyethers,polyether amides, polyether esters, and copolymers thereof. Examples ofsuitable polyacrylates include poly(methyl methacrylate), poly(ethylmethacrylate), ply(butyl methacrylate), poly(isobutyl methacrylate),poly(hexyl methacrylate), poly(isodecyl methacrylate), poly(laurylmethacrylate), poly(phenyl methacrylate), poly(methyl acrylate),poly(isopropyl acrylate), poly(isobutyl acrylate) and poly(octadecylacrylate). Examples of other suitable polymers include polystyrene,polypropylene, polyvinyl phenol, polyvinylpyrrolidone, chlorinatedpolybutylene, poly(octadecyl vinyl ether) ethylene vinyl acetate,polyethylene, poly(ethylene oxide)-poly(ethylene terephthalate),polyethylene/nylon (graft copolymer), polycaprolactones-polyamide (blockcopolymer), poly(caprolactone) dimethacrylate-n-butyl acrylate,poly(norbornyl-polyhedral oligomeric silsequioxane), polyvinylchloride,urethane/butadiene copolymers, polyurethane block copolymers,styrene-butadiene-styrene block copolymers, and the like.

The shape memory polymer or the shape memory alloy, may be activated byany suitable means, preferably a means for subjecting the material to atemperature change above, or below, a transition temperature. Forexample, for elevated temperatures, heat may be supplied using hot gas(e.g., air), steam, hot liquid, or electrical current. The activationmeans may, for example, be in the form of heat conduction from a heatedelement in contact with the shape memory material, heat convection froma heated conduit in proximity to the thermally active shape memorymaterial, a hot air blower or jet, microwave interaction, resistiveheating, and the like. In the case of a temperature drop, heat may beextracted by using cold gas, or evaporation of a refrigerant. Theactivation means may, for example, be in the form of a cool room orenclosure, a cooling probe having a cooled tip, a control signal to athermoelectric unit, a cold air blower or jet, or means for introducinga refrigerant (such as liquid nitrogen) to at least the vicinity of theshape memory material.

Suitable magnetic materials include, but are not intended to be limitedto, soft or hard magnets; hematite; magnetite; magnetic material basedon iron, nickel, and cobalt, alloys of the foregoing, or combinationscomprising at least one of the foregoing, and the like. Alloys of iron,nickel and/or cobalt, can comprise aluminum, silicon, cobalt, nickel,vanadium, molybdenum, chromium, tungsten, manganese and/or copper.

Suitable MR fluid materials include, but are not intended to be limitedto, ferromagnetic or paramagnetic particles dispersed in a carrierfluid. Suitable particles include iron; iron alloys, such as thoseincluding aluminum, silicon, cobalt, nickel, vanadium, molybdenum,chromium, tungsten, manganese and/or copper; iron oxides, includingFe₂O₃ and Fe₃O₄; iron nitride; iron carbide; carbonyl iron; nickel andalloys of nickel; cobalt and alloys of cobalt; chromium dioxide;stainless steel; silicon steel; and the like. Examples of suitableparticles include straight iron powders, reduced iron powders, ironoxide powder/straight iron powder mixtures and iron oxide powder/reducediron powder mixtures. A preferred magnetic-responsive particulate iscarbonyl iron, preferably, reduced carbonyl iron.

The particle size should be selected so that the particles exhibitmulti-domain characteristics when subjected to a magnetic field. Averagedimension sizes for the particles can be less than or equal to about1,000 micrometers, with less than or equal to about 500 micrometerspreferred, and less than or equal to about 100 micrometers morepreferred. Also preferred is a particle dimension of greater than orequal to about 0.1 micrometer, with greater than or equal to about 0.5more preferred, and greater than or equal to about 10 micrometersespecially preferred. The particles are preferably present in an amountbetween about 5.0 to about 50 percent by volume of the total MR fluidcomposition.

Suitable carrier fluids include organic liquids, especially non-polarorganic liquids. Examples include, but are not limited to, siliconeoils; mineral oils; paraffin oils; silicone copolymers; white oils;hydraulic oils; transformer oils; halogenated organic liquids, such aschlorinated hydrocarbons, halogenated paraffins, perfluorinatedpolyethers and fluorinated hydrocarbons; diesters; polyoxyalkylenes;fluorinated silicones; cyanoalkyl siloxanes; glycols; synthetichydrocarbon oils, including both unsaturated and saturated; andcombinations comprising at least one of the foregoing fluids.

The viscosity of the carrier component can be less than or equal toabout 100,000 centipoise, with less than or equal to about 10,000centipoise preferred, and less than or equal to about 1,000 centipoisemore preferred. Also preferred is a viscosity of greater than or equalto about 1 centipoise, with greater than or equal to about 250centipoise preferred, and greater than or equal to about 500 centipoiseespecially preferred.

Aqueous carrier fluids may also be used, especially those comprisinghydrophilic mineral clays such as bentonite or hectorite. The aqueouscarrier fluid may comprise water or water comprising a small amount ofpolar, water-miscible organic solvents such as methanol, ethanol,propanol, dimethyl sulfoxide, dimethyl formamide, ethylene carbonate,propylene carbonate, acetone, tetrahydrofuran, diethyl ether, ethyleneglycol, propylene glycol, and the like. The amount of polar organicsolvents is less than or equal to about 5.0% by volume of the total MRfluid, and preferably less than or equal to about 3.0%. Also, the amountof polar organic solvents is preferably greater than or equal to about0.1%, and more preferably greater than or equal to about 1.0% by volumeof the total MR fluid. The pH of the aqueous carrier fluid is preferablyless than or equal to about 13, and preferably less than or equal toabout 9.0. Also, the pH of the aqueous carrier fluid is greater than orequal to about 5.0, and preferably greater than or equal to about 8.0.

Natural or synthetic bentonite or hectorite may be used. The amount ofbentonite or hectorite in the MR fluid is less than or equal to about 10percent by weight of the total MR fluid, preferably less than or equalto about 8.0 percent by weight, and more preferably less than or equalto about 6.0 percent by weight. Preferably, the bentonite or hectoriteis present in greater than or equal to about 0.1 percent by weight, morepreferably greater than or equal to about 1.0 percent by weight, andespecially preferred greater than or equal to about 2.0 percent byweight of the total MR fluid.

Optional components in the MR fluid include clays, organoclays,carboxylate soaps, dispersants, corrosion inhibitors, lubricants,extreme pressure anti-wear additives, antioxidants, thixotropic agentsand conventional suspension agents. Carboxylate soaps include ferrousoleate, ferrous naphthenate, ferrous stearate, aluminum di- andtri-stearate, lithium stearate, calcium stearate, zinc stearate andsodium stearate, and surfactants such as sulfonates, phosphate esters,stearic acid, glycerol monooleate, sorbitan sesquioleate, laurates,fatty acids, fatty alcohols, fluoroaliphatic polymeric esters, andtitanate, aluminate and zirconate coupling agents and the like.Polyalkylene diols, such as polyethylene glycol, and partiallyesterified polyols can also be included.

Suitable MR elastomer materials include, but are not intended to belimited to, an elastic polymer matrix comprising a suspension offerromagnetic or paramagnetic particles, wherein the particles aredescribed above. Suitable polymer matrices include, but are not limitedto, poly-alpha-olefins, natural rubber, silicone, polybutadiene,polyethylene, polyisoprene, and the like.

Electroactive polymers include those polymeric materials that exhibitpiezoelectric, pyroelectric, or electrostrictive properties in responseto electrical or mechanical fields. The materials generally employ theuse of compliant electrodes that enable polymer films to expand orcontract in the in-plane directions in response to applied electricfields or mechanical stresses. An example of an electrostrictive-graftedelastomer with a piezoelectric poly(vinylidenefluoride-trifluoro-ethylene) copolymer. This combination has the abilityto produce a varied amount of ferroelectric-electrostrictive molecularcomposite systems. These may be operated as a piezoelectric sensor oreven an electrostrictive actuator. Activation of an EAP based padpreferably utilizes an electrical signal to provide change in shapeorientation sufficient to provide displacement. Reversing the polarityof the applied voltage to the EAP can provide a reversible lockdownmechanism.

Materials suitable for use as the electroactive polymer may include anysubstantially insulating polymer or rubber (or combination thereof) thatdeforms in response to an electrostatic force or whose deformationresults in a change in electric field. Exemplary materials suitable foruse as a pre-strained polymer include silicone elastomers, acrylicelastomers, polyurethanes, thermoplastic elastomers, copolymerscomprising PVDF, pressure-sensitive adhesives, fluoroelastomers,polymers comprising silicone and acrylic moieties, and the like.Polymers comprising silicone and acrylic moieties may include copolymerscomprising silicone and acrylic moieties, polymer blends comprising asilicone elastomer and an acrylic elastomer, for example.

Materials used as an electroactive polymer may be selected based on oneor more material properties such as a high electrical breakdownstrength, a low modulus of elasticity—(for large or small deformations),a high dielectric constant, and the like. In one embodiment, the polymeris selected such that is has an elastic modulus at most about 100 MPa.In another embodiment, the polymer is selected such that is has amaximum actuation pressure between about 0.05 MPa and about 10 MPa, andpreferably between about 0.3 MPa and about 3 MPa. In another embodiment,the polymer is selected such that is has a dielectric constant betweenabout 2 and about 20, and preferably between about 2.5 and about 12. Thepresent disclosure is not intended to be limited to these ranges.Ideally, materials with a higher dielectric constant than the rangesgiven above would be desirable if the materials had both a highdielectric constant and a high dielectric strength. In many cases,electroactive polymers may be fabricated and implemented as thin films.Thicknesses suitable for these thin films may be below 50 micrometers.

As electroactive polymers may deflect at high strains, electrodesattached to the polymers should also deflect without compromisingmechanical or electrical performance. Generally, electrodes suitable foruse may be of any shape and material provided that they are able tosupply a suitable voltage to, or receive a suitable voltage from, anelectroactive polymer. The voltage may be either constant or varyingover time. In one embodiment, the electrodes adhere to a surface of thepolymer. Electrodes adhering to the polymer are preferably compliant andconform to the changing shape of the polymer. Correspondingly, thepresent disclosure may include compliant electrodes that conform to theshape of an electroactive polymer to which they are attached. Theelectrodes may be only applied to a portion of an electroactive polymerand define an active area according to their geometry. Various types ofelectrodes suitable for use with the present disclosure includestructured electrodes comprising metal traces and charge distributionlayers, textured electrodes comprising varying out of plane dimensions,conductive greases such as carbon greases or silver greases, colloidalsuspensions, high aspect ratio conductive materials such as carbonfibrils and carbon nanotubes, and mixtures of ionically conductivematerials.

Materials used for electrodes of the present disclosure may vary.Suitable materials used in an electrode may include graphite, carbonblack, colloidal suspensions, thin metals including silver and gold,silver filled and carbon filled gels and polymers, and ionically orelectronically conductive polymers. It is understood that certainelectrode materials may work well with particular polymers and may notwork as well for others. By way of example, carbon fibrils work wellwith acrylic elastomer polymers while not as well with siliconepolymers.

The active material may also comprise a piezoelectric material. Also, incertain embodiments, the piezoelectric material may be configured as anactuator for providing rapid deployment. As used herein, the term“piezoelectric” is used to describe a material that mechanically deforms(changes shape) when a voltage potential is applied, or conversely,generates an electrical charge when mechanically deformed. Employing thepiezoelectric material will utilize an electrical signal for activation.Upon activation, the piezoelectric material can cause displacement inthe powered state. Upon discontinuation of the activation signal, thestrips will assume its original shape orientation, e.g., a straightenedshape orientation.

Preferably, a piezoelectric material is disposed on strips of a flexiblemetal or ceramic sheet. The strips can be unimorph or bimorph.Preferably, the strips are bimorph, because bimorphs generally exhibitmore displacement than unimorphs.

One type of unimorph is a structure composed of a single piezoelectricelement externally bonded to a flexible metal foil or strip, which isstimulated by the piezoelectric element when activated with a changingvoltage and results in an axial buckling or deflection as it opposes themovement of the piezoelectric element. The actuator movement for aunimorph can be by contraction or expansion. Unimorphs can exhibit astrain of as high as about 10%, but generally can only sustain low loadsrelative to the overall dimensions of the unimorph structure. Duringmanufacture of an actuator, a ceramic layer, an adhesive layer, and afirst pre-stress layer are simultaneously heated to a temperature abovethe melting point of the adhesive, and then subsequently allowed tocool, thereby re-solidifying and setting the adhesive layer. During thecooling process the ceramic layer becomes strained, due to the highercoefficients of thermal contraction of the metal pre-stress layer andthe adhesive layer than of the ceramic layer. Also, due to the greaterthermal contraction of the laminate materials than the ceramic layer,the ceramic layer deforms into an arcuate shape having a generallyconcave face.

In contrast to the unimorph piezoelectric device, a bimorph deviceincludes an intermediate flexible metal foil sandwiched between twopiezoelectric elements. Bimorphs exhibit more displacement thanunimorphs because under the applied voltage one ceramic element willcontract while the other expands. Bimorphs can exhibit strains up toabout 20%, but similar to unimorphs, generally cannot sustain high loadsrelative to the overall dimensions of the unimorph structure.

Suitable piezoelectric materials include inorganic compounds, organiccompounds, and metals. With regard to organic materials, all of thepolymeric materials with non-centrosymmetric structure and large dipolemoment group(s) on the main chain or on the side-chain, or on bothchains within the molecules, can be used as candidates for thepiezoelectric film. Examples of suitable polymers include, for example,but are not limited to, poly(sodium 4-styrenesulfonate) (“PSS”), polyS-119 (poly(vinylamine)backbone azo chromophore), and their derivatives;polyfluorocarbons, including polyvinylidene fluoride (“PVDF”), itsco-polymer vinylidene fluoride (“VDF”), trifluoroethylene (TrFE), andtheir derivatives; polychlorocarbons, including poly(vinyl chloride)(“PVC”), polyvinylidene chloride (“PVDC”), and their derivatives;polyacrylonitriles (“PAN”), and their derivatives; polycarboxylic acids,including poly(methacrylic acid (“PMA”), and their derivatives;polyureas, and their derivatives; polyurethanes (“PU”), and theirderivatives; bio-polymer molecules such as poly-L-lactic acids and theirderivatives, and membrane proteins, as well as phosphate bio-molecules;polyanilines and their derivatives, and all of the derivatives oftetramines; polyimides, including Kapton molecules and polyetherimide(“PEI”), and their derivatives; all of the membrane polymers;poly(N-vinyl pyrrolidone) (“PVP”) homopolymer, and its derivatives, andrandom PVP-co-vinyl acetate (“PVAc”) copolymers; and all of the aromaticpolymers with dipole moment groups in the main-chain or side-chains, orin both the main-chain and the side-chains, and mixtures thereof.

Further, piezoelectric materials can include Pt, Pd, Ni, Ti, Cr, Fe, Ag,Au, Cu, and metal alloys and mixtures thereof. These piezoelectricmaterials can also include, for example, metal oxide such as SiO₂,Al₂O₃, ZrO₂, TiO₂, SrTiO₃, PbTiO₃, BaTiO₃, FeO₃, Fe₃O₄, ZnO, andmixtures thereof; and Group VIA and IIB compounds, such as CdSe, CdS,GaAs, AgCaSe 2, ZnSe, GaP, InP, ZnS, and mixtures thereof.

Advantageously, the above noted hood lift mechanisms utilizing theactive materials described herein provide relatively robust systemscompared to prior art lift mechanisms. In addition to providingreversibility, the active material based actuators are relativelycompact and are of significantly lower weight. Furthermore, it should berecognized by those skilled in the art that the hood lift mechanisms, asused herein, might be configured to allow for, among others, increasedease of operation and more energy to be absorbed during an impact event.It should also be recognized by those skilled in the art that the activematerials, as used herein, allow input from crash sensors, pre-crashsensors and built-in logic systems, in general.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiments disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the presentapplication.

1. A cam lift and reset assembly, comprising: a cam mounted on arotatable shaft having a cam profile effective to provide a liftingforce to a contacted part thereon upon rotation of the shaft andmovement of the cam profile of the cam relative to the contacted partfrom a rest position to a lift position; an active material in operativecommunication with the shaft, the active material being operative tochange at least one property of the active material in response to anactivation signal so as to effect rotation of the shaft; and a resetdevice in operative communication with the shaft to provide a resetforce to the contacted part and counter-rotation of the shaft andmovement of the cam profile of the cam relative to the contacted partfrom the lift position to the rest position.
 2. The cam lift and resetassembly of claim 1, wherein the active material comprises a torsionalspring formed of a shape memory alloy disposed on the shaft.
 3. The camlift and reset assembly of claim 2, wherein the shape memory alloycontracts upon activation to effect rotation of the shaft.
 4. The camlift and reset assembly of claim 1, wherein the reset device comprises apassive device that stores energy during rotation of the shaftsufficient to provide the reset force and counter rotation of the shaft.5. The cam lift and reset assembly of claim 4, wherein the reset devicecomprises a spring.
 6. The cam lift and reset assembly of claim 5,wherein the reset device comprises a torsional spring disposed on theshaft.
 7. The cam lift and reset assembly of claim 5, wherein the resetdevice comprises a linear spring disposed on the cam.
 8. The cam liftand reset assembly of claim 1, wherein the reset device comprises anactive device that provide the reset force and counter rotation of theshaft by activation of a second active material.
 9. The cam lift andreset assembly of claim 8, wherein the second active material is inoperative communication with the rotating shaft, the second activematerial being operative to change at least one property of the activematerial in response to an activation signal so as to effectcounter-rotation of the shaft.
 10. The cam lift and reset assembly ofclaim 9, wherein the shape memory alloy contracts upon activation toeffect counter-rotation of the shaft.
 11. The cam lift and resetassembly of claim 8, wherein the second active material comprises atorsional spring formed of a second shape memory alloy disposed on theshaft.
 12. The cam lift and reset assembly of claim 1, wherein thecontacted part is a hood.
 13. The cam lift and reset assembly of claim1, further comprising at least one sensor and a controller in operativecommunication with the active material.
 14. A process for operating acam lift and reset assembly that comprises a cam mounted on a rotatableshaft and having a cam profile; an active material in operativecommunication with the shaft; and a reset device in operativecommunication with the shaft, comprising: sensing a condition;activating the active material in response to the sensed condition toeffect rotation of the shaft; using the rotation of the shaft to providea lifting force to a contacted part thereon and movement of the camprofile of the cam relative to the contacted part; raising the contactedpart from a rest position to a lift position; activating the resetdevice to effect counter-rotation of the shaft; using thecounter-rotation of the shaft to provide a reset force to the contactedpart thereon and movement of the cam profile of the cam relative to thecontacted part; and lowering the contacted part from the lift positionto the rest position.
 15. The process of claim 14, further comprisingsensing a second condition, and activating the reset device in responseto the second condition.
 16. The process of claim 15, wherein the resetdevice comprises a passive device that stores energy during rotation ofthe shaft sufficient to provide the reset force and counter rotation ofthe shaft.
 17. The process of claim 16, wherein the reset devicecomprises a spring.
 18. The process of claim 14, wherein the resetdevice comprises an active device that provides the reset force andcounter rotation of the shaft by activation of a second active material.19. The process of claim 18, wherein the second active material is inoperative communication with the rotating shaft, the second activematerial being operative to change at least one property of the activematerial in response to an activation signal so as to effectcounter-rotation of the shaft.
 20. The process of claim 19, wherein thesecond active material comprises a torsional spring formed of a secondshape memory alloy disposed on the shaft.